Method of controlling a segmented flash system

ABSTRACT

The invention describes a method of controlling a segmented flash ( 10 ) having a plurality of flash segments (S 1 , S 2 , . . . , Sn), which method comprises the steps of measuring the forward voltages (Vf 1 , Vf 2 , . . . , Vfn) of the flash segments (S 1 , S 2 , . . . , Sn); and adjusting the brightness of the flash segments (S 1 , S 2 , . . . , Sn) on the basis of the measured forward voltages (Vf 1 , Vf 2 , . . . , Vfn) to achieve a desired illumination profile (P) for the segmented flash ( 10 ). The invention further describes a segmented flash system ( 1 ) comprising a segmented flash ( 10 ) with a plurality of flash segments (S 1 , S 2 , . . . , Sn), wherein each flash segment (S 1 , S 2 , . . . , Sn) is arranged to illuminate a portion ( 20 ) of a scene ( 2 ); and a flash driver ( 11 ) adapted to perform the steps of the inventive method to adjust the brightness of the flash segments (S 1 , S 2 , . . . , Sn).

FIELD OF THE INVENTION

The invention describes a method of controlling a segmented flashsystem. The invention also describes a segmented flash system.

BACKGROUND OF THE INVENTION

When a conventional flash system is used in photographing a scene, anyobjects that are too close to the camera may suffer from overexposureand appear too “white” or pale in the image, while objects further awayfrom the camera may not be sufficiently illuminated and appear too darkin the photograph or image. Developments in flash systems have led to asegmented flash, i.e. a flash made up of an array of light sources. Thespectra of the light sources deployed in the segmented flash can bechosen to achieve a desired white balance. Each light source illuminatesa region of the scene, so that the segmented flash generates an“illumination profile” or pattern. It is possible to determine therelative amount of light required to correctly illuminate or expose eachregion of the scene, for example by obtaining a depth map using asuitable technique such as time-of-flight (ToF), triangulation, stereovision, structured light, interferometry etc., and to use thisinformation to determine an optimal illumination profile. With suchoptimal illumination profile, objects located further from the camerawill receive higher light intensities, while objects located closer tothe camera will receive less light.

Each flash segment has an LED or other appropriate light source, and theflash segments are individually controllable. The complete illuminationprofile is achieved by driving each flash segment at an appropriatecurrent level. This is generally achieved by using an appropriate driverthat is realized to drive the flash segments with the correct relativeand absolute current levels.

However, a problem associated with the known segmented flash systems isthe possible occurrence of a relative spectrum shift of one or moresegments as a result of different segment temperatures. Differenttemperatures in the flash segments may be the result of differentcurrent driving levels in a previous flash event for which differentrequired levels of light intensity were used according to a depth map toilluminate the different scene regions. For example, one or moresegments may have been used to strongly illuminate a scene region, andthese flash segments will be hotter than other flash segments that wereused to only moderately or weakly illuminate other scene regions.Temperature differences may also occur as a result of different thermalbehaviour of the different segments. The problem arises to some extentfrom the prior art approach of assuming an equilibrium condition fortemperature when calculating the drive currents for the flash segments.However, any preceding flash event that used unequal drive currents toachieve correct illumination of the previous scene will disturb any suchtemperature equilibrium at least for a certain duration following aflash event. Any subsequent flash event within this duration may beassociated with a spectrum shift that can result in an unwanted andperceptible colourization of the image, particularly since the human eyeis able to detect even only very slight colour variations or nuancesaround white colour points and skin colour points.

Therefore, it is an object of the invention to provide an improved wayof driving a segmented flash to overcome the problems outlined above.

SUMMARY OF THE INVENTION

The object of the invention is achieved by the method of claim 1 ofcontrolling a flash system; any by the segmented flash system of claim10.

According to the invention, the method of controlling a flash systemhaving a plurality of flash segments comprises the steps of measuringthe forward voltages of the flash segments prior to a flash event and/orfollowing a flash event; and subsequently adjusting the brightness ofthe flash segments on the basis of the measured forward voltages toachieve a desired illumination profile.

In the context of the invention, the expressions “segmented flash” and“matrix flash” may be regarded as synonyms and may be usedinterchangeably in the following. An advantage of the inventive methodis that it is effective in compensating the unwanted colour shiftdescribed in the introduction. Any temperature differences between theflash segments, arising as the result of different current drivinglevels, can be detected and then corrected. The method thereforeprovides a straightforward way of suppressing or even eliminating such acolour shift.

In a segmented flash, each flash segment can have a differenttemperature and a different temperature characteristic, and theresulting differences in temperature hysteresis for the various segmentsmeans that a prior art method will be unable to always generate acorrect illumination profile. In the inventive method, a correctillumination profile can always be ensured by measuring the forwardvoltages of the flash segments (preferably just prior to a flash event)and then adjusting the brightness of each individual flash segmentaccordingly. This can be done by adjusting the current to each segment,by adjusting the duty cycles of the individual segments, or byscheduling a dummy flash, as will be explained below.

According to the invention, the segmented flash system comprises aplurality of flash segments arranged in a flash matrix, wherein eachflash segment is arranged to illuminate a portion of a scene. The flashsystem further comprises a flash driver adapted to perform the steps ofthe inventive method to equalize the temperatures of the flash segments.The flash driver can be controlled by a suitable processor that isrealised to determine the optimum current settings based on the forwardvoltage measurements provided by the flash driver.

The dependent claims and the following description disclose particularlyadvantageous embodiments and features of the invention. Features of theembodiments may be combined as appropriate. Features described in thecontext of one claim category can apply equally to another claimcategory.

Any suitable light sources—or any suitable combination of differentlight sources—may be used in a segmented flash, for examplesemiconductor light sources such as light-emitting diodes (LEDs) orvertical cavity surface emitting lasers (VCSELs). In the following, butwithout restricting the invention in any way, it may be assumed thatLEDs are used as the light sources or “emitters” of a segmented flash orflash matrix. For an application such as a camera flash of a mobiledevice, for example, the total power of the LEDs may be in the region of6 W, and any suitable sized array may be used, for example a 3×3 array,a 5×5 array, a 15×21 array, etc. The array shape can be square,rectangular, circular, etc. The terms “LED” and “emitter” may be usedinterchangeably in the following. The emitters of the segmented flashcan emit in the visible range, but may alternatively emit in theinfrared or ultraviolet range, depending on the application.

The invention is based on the insight that the forward voltage acrossthe forward biased LED(s) of a flash segment is directly related to thetemperature of the LED(s), and that any temperature difference betweenflash segments will result in a voltage differential, which willmanifest as a corresponding light output and/or colour shift. Some ofall of the flash segments may preferably comprise a plurality of LEDs.In some or all of the segments, the LEDs may preferably have differentspectra, chosen to achieve a correct adaptation to the ambient lightinglevels or to a desired colour temperature. Preferably, all segments havethe same or essentially the same combination of spectra.

A camera—or any apparatus or device that incorporates a camera—may alsocomprise an embodiment of the inventive segmented flash system. Forexample, a device incorporating a camera may be a mobile phone, a tabletcomputer, etc.

The inventive segmented flash system preferably comprises a depth mapmodule that is realized to determine a depth map or 3D profile of ascene. The depth map module is preferably also realised to determine therelative amount of light required to illuminate each portion of thescene. In this way, it is possible to determine the required intensityfor each scene region in order to determine the optimal illuminationprofile for the overall scene.

The severity of a temperature-related colour shift or colourizationartefact depends on several factors such as the type of emitters and thecolour points of the emitters used in the segmented flash; the thermalresistances between the individual emitters and a base or carrier towhich they are mounted; the time interval between flashes; thealteration of emitter optical parameters as a function of temperature;the nature of the scene to be imaged, etc. Assuming a uniformly whitescene is to be imaged, any colour shift in the “white scene” can beexpressed as a change in the chromaticity coordinates. Preferably, anyalteration in the chromaticity coordinates (expressed as du‘v’ usingCIELUV notation) preferably does not exceed a specified threshold (e.g.0.005 in CIELUV colour space). Of course, any suitable camera colourspace system could be used as well.

In a preferred embodiment of the invention, the forward voltages of theflash segments are monitored prior to every flash event, and a suitablecorrective measure is taken to ensure that any flash event will be ableto provide the optimal illumination profile. This will ensure thatcolorization artefacts will be essentially completely avoided.

Prior art devices assume that the temperatures of the flash segmentswill return to equilibrium after a short while, for example within acertain length of time after the user has stopped taking pictures.However, the inventive method ensures that such assumptions need not bemade, and always set the correct currents per segments by monitoring theactual temperature of each segment and taking the temperatures intoaccount.

Preferably, the step of measuring the forward voltages of the flashsegments is performed under identical low constant current conditions. Alow measurement current is used to ensure that the measurement itselfdoes not disturb or falsify the actual temperature distribution. The lowcurrent also ensures that the segments are not self-heated during themeasurement, as well as keeping energy consumption to a minimum.Measuring the forward voltages is a favourably straightforward way ofobtaining the desired information, and is easier than directly measuringthe absolute temperatures of the segments, which would require a precisecalibration step for each LED. Preferably, the forward voltages aremeasured after a certain time has elapsed after a flash event. The timeinstant at which the forward voltages are measured may depend to someextent on the physical and thermal characteristics of the emitters usedin the segmented flash.

In addition, the forward voltage monitoring can be applied for aself-test function to detect flash failures. Any flash segment that isopen or shorted will be detected during the step of monitoring theforward voltages. The controller can take any faulty LED into accountwhen computing the illumination profile for the remaining healthy LEDsof the segmented flash. Such a detected error condition may be reportedto a user, for example as a warning on the screen of the device, or asan error log stored in a memory that can be read out during service orrepair.

The measured forward voltages of the flash segments are analog valueswhich are preferably converted to digital values which can be used by asuitable microprocessor to calculate the drive currents required toachieve a desired white balance for a subsequent flash event takingplace within a certain time window. For example, an embodiment of asegmented flash may be characterized by a certain time window for areturn to a temperature equilibrium state after a flash event. Theduration of that time window will depend to some extent on the physicaland thermal characteristics of the implemented flash emitters.Therefore, the driver of that segmented flash may implement anycorrective measures for a subsequent flash event that takes place withinthat time window.

After obtaining the measurements for the forward voltages, the driver ofthe inventive segmented flash system can determine a suitable correctivemeasure. For example, in a particularly preferred embodiment of theinvention, the driver computes a drive current for each individual flashsegment on the basis of the differences between the measured forwardvoltages. In a very simple exemplary case, the segmented flash systemmay comprise a two-by-two array of four segments. After a flash eventused to illuminate a scene for which one of the segments was used toilluminate an object far away from the camera, three of the flashsegments have an essentially equivalent measured forward voltage, whilethe fourth flash segment has a lower forward voltage due to the highertemperature. For a subsequent flash event, current ratios of the flashsegments are adjusted. Using the simple example above, the drive currentfor the three “cool” flash segments is lowered while the drive currentfor the fourth (“hot”) flash segment is raised in order to achieve thecorrect illuminance distribution and to correct the colour point in asubsequent scene, even if there is a temperature differential across theflash segments. Correction of the colour point is particularlyfavourable in the case of “tuneable” camera flash systems, for example asegmented flash comprising LEDs with two distinct colour points.

Alternatively or in addition, a corrective measure may comprise a stepof determining flash timing (i.e. “flash firing”) for the individualflash segments. Instead of tuning the amplitude of the current persegment, the duty cycle per segment can be used for flash firing in theblanking period (the time interval during the integration time of thesensor). It can also be used during integration time if matched to theintegration time of the image sensor. In such an embodiment of theinventive method, firing of the flash segments is timed on the basis ofthe information obtained from the forward voltage monitoring step. Forexample, a flash segment that is still hot from a previous flash andhaving a corresponding lower forward voltage event may be timed to beactive for slightly longer-duty cycle in order to deliver the requiredlight output during a flash event. Similarly, flash segments that arecooler may be timed to be active for slightly shorter duration. Theillumination distribution can be favourably achieved or in case of amultiple coloured flash having LEDs with more than one colour point—thecolour characteristics of the scene can be favourably preserved by sucha step of individually timing the flash segments.

The corrective measure(s) described above may be applied when the userof the camera initiates a subsequent flash event, i.e. when the camerais being actively used to capture an image of the scene. Such a flashevent is referred to in the following as an “active” flash event.Alternatively, in a further preferred embodiment of the invention, thestep of equalizing the temperatures of the flash segments comprises thescheduling of a “dummy” flash event. This dummy flash event is not usedby the camera to capture an image of the scene, i.e. it is scheduledoutside the integration period of the image sensor. Preferably, themethod comprises a step of determining a drive current distribution forthe flash segments in the preceding flash event and applying thecomplement of the drive current distribution for the dummy flash event.A dummy flash is preferably timed to lie outside the exposure intervalof the image sensor so that overexposure of an actively captured imagewill not result. For example, the time interval between a flash eventand a dummy flash event is at most 200 ms, preferably at most 50 ins ifthe camera refresh rate allows this.

In a preferred embodiment of the invention, the flash driver comprises astate machine to efficiently manage the forward voltage measurementsteps (the use of a state machine for this purpose can reduce processorload and serial bus loading); a multiplexer configured to select aspecific flash segment; an analog-to-digital converter adapted toconvert the measured forward voltages into digital values fortransferring via a serial bus for example, and a storage means such as anumber of registers for temporarily storing the converted forwardvoltage values.

Other objects and features of the present invention will become apparentfrom the following detailed descriptions considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are designed solely for the purposes of illustration and not asa definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified block diagram of an embodiment of theinventive segmented flash system;

FIG. 2 shows an embodiment of a prior art segmented flash system;

FIG. 3 shows a more detailed block diagram of an embodiment of theinventive segmented flash system;

FIGS. 4 and 5 show embodiments of a segmented flash;

FIG. 6 shows an illumination profile in relation to a correspondingscene;

FIGS. 7-9 show successive flash events scheduled using an embodiment ofthe inventive method;

FIG. 10 shows successive flash events scheduled using a prior artmethod.

In the drawings, like numbers refer to like objects throughout. Objectsin the diagrams are not necessarily drawn to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows a simplified block diagram of an embodiment of theinventive segmented flash system 1. The diagram shows a segmented flash10, in this case a 5×5 square array of LEDs 100. The LEDs 100 of thisarray will illuminate twenty-five regions in a scene. In this exemplaryembodiment, an illumination profile P can be provided by a depth mapmodule 1B, which may for example compute the illumination profile Pusing information obtained by a photodetector 4. The illuminationprofile P specifies the required intensity or power required for eachLED 100 to correctly illuminate the scene, assuming an equilibriumcondition in which all LEDs 100 have essentially the same temperature.In this exemplary embodiment, the segmented flash system 1 alsocomprises a voltage measuring module 1A that measures the forwardvoltages Vf1, Vf2, . . . , Vfn of the LEDs 100 of the array. With thisinformation, a controller 1C computes adjusted drive current valuesId1_a, Id2_a, . . . , Idn_a for the LEDs 100 of the array. Each adjusteddrive current value Id1_a, Id2_a, . . . , Idn_a takes into considerationthe required intensity for the corresponding LED 100, but also itstemperature (which is related to forward voltage in a well-definedmanner). Therefore, even if the flash has recently been used, resultingin an uneven temperature distribution over the array, the controller 1Cis able to compute adjusted drive current values Id1_a, Id2_a, . . . ,Idn_a which will result in the desired illumination and which willreduce or even eliminate any undesirable temperature-related illuminancedifference and/or colour shift.

FIG. 2 shows an embodiment of a prior art segmented flash system 3. Herealso, a segmented flash 10 comprises a 5×5 square array of LEDs 100. Theprior art flash system 3 also uses a depth map module to compute anillumination profile P from the feedback provided by an image sensor,and forwards this to a controller 320. The illumination profile Pspecifies the required intensity or power required for each LED 100 tocorrectly illuminate the scene, but assumes an equilibrium condition inwhich all LEDs 100 have essentially the same temperature. However, asexplained above, if the flash has recently been used, there may be anuneven temperature distribution over the array, resulting in anundesirable colour shift in the image captured with the subsequent flashevent.

FIG. 3 shows a more detailed block diagram of an embodiment of theinventive segmented flash system 1 of FIG. 1. The diagram shows relevantblocks or modules in a flash driver 11 that drives the LEDs of asegmented flash 10. In this exemplary embodiment, the flash driver 11comprises a multiplexer 111 configured to connect a specific flashsegment S1, S2, . . . , Sn to an analog-to-digital converter 112 so thatthe forward voltage Vf1, Vf2, . . . , Vfn of the selected flash segmentS1, S2, . . . , Sn can be converted to a digital value; and a number ofregisters 113 to store the digital values. These blocks 111, 112, 113fulfil the function of the voltage measuring module 1A of FIG. 1. Eachflash segment is also connected to a current sink 114. An illuminationprofile P is computed by a suitable processor unit 120 for a subsequentflash event on the basis of the measured forward voltages Vf1, Vf2, . .. , Vfn. The illumination profile P can be a set of drive current valuesfor the subsequent flash event. These are stored in a memory 116,converted by a digital-to-analog converter 115 and then applied to thecurrent sinks 114 during the subsequent flash event. The timing of thevarious blocks can be controlled using a clock oscillator 118 and acounter 119, as will be known to the skilled person. Communication withthe processor unit 120 can be done over a suitable interface 117 such asan I²C interface. The processor unit 120 and its related blocks 114,115, 118, 119 etc. fulfil the function of the depth map module 1B andthe controller 1C of FIG. 1. The processor unit 120 computes theamplitude and/or timing of a drive current Id1_a, Id2_a, . . . Idn_a toachieve the desired illumination profile P. A state machine 110 is usedto control the related blocks. The forward voltages Vf1, Vf2, . . . ,Vfn are preferably measured prior to each flash event, and the adjusteddrive currents Id1_a, Id2_a, . . . Idn_a are used if a successive flashevent takes place during a time interval that is shorter than the timeneeded for the array to return to an equilibrium state as regardstemperature.

FIGS. 4 and 5 show embodiments of a segmented flash 10 that can bedriven by the driver 11 of FIG. 3. In FIG. 4, each flash segment S1, S2,. . . , Sn comprises one LED 100. In FIG. 5, each flash segment S1, S2,. . . Sn comprises two LEDs 100A, 100B. The LEDs 100A, 100B can havedifferent spectra. In these embodiments, the LEDs are all driven inparallel. An alternative realisation could use row or column scanning ofthe matrix, thereby requiring a smaller number of interconnects and asmaller number of current sources in the driver circuit.

FIG. 6 shows a scene 2 and a corresponding illumination profile P. Here,the scene 2 shows two figures, one of which is closer to the camera, andone of which is further away. The figure on the left will need lessillumination that the figure on the right in order to correctlyilluminate the scene 2. This can be determined using a time-of-flighttechnique, and the resulting depth map is used to generate the optimalillumination profile P. Using the 5×5 segmented flash described above,three of the LEDs will be driven at a higher power (these are shown bythe light squares in the illumination profile P), and three of the LEDswill be driven at a lower power (these are shown by the darkest squaresin the illumination profile P). The difference in intensity or powerwill result in a temperature differential over the segmented array, andit may take some time for the array to return to a temperatureequilibrium state. In the prior art approach, if a subsequent flashevent takes place in that time, a colour shift may become apparent inthe image. Using the inventive method, the adjusted drive currents arecomputed to compensate for any such temperature differential, and therewill not be any noticeable colour shift in an image captured with asubsequent flash event.

FIGS. 7-9 show successive flash events scheduled using an embodiment ofthe inventive method. For the sake of simplicity, it is assumed that thesame scene is being photographed during each flash event, and that theillumination profile is the same for both scenes (of course, the sceneand the corresponding illumination profile may be different). To keepthe explanation simple, only two LEDs are considered in each case,namely the LEDs with the highest and lowest intensities. In the firstflash event, one LED receives a relatively high drive current Id1, andthe other LED receives a relatively low drive current Id2. The time Teqrequired for the segmented flash to return to an equilibrium conditionis indicated in the diagram. Prior to each subsequent flash event, attime t_(m), the forward voltages of the flash segments are measured. InFIG. 7, the drive currents in the subsequent flash event are adjusted tocorrect for any temperature differential detected by discrepancies inthe forward voltage values Vf1, Vf2, . . . , Vfn. Here, the LED thatreceived the highest drive current Id1 in the first event E will, in thesubsequent event E, receive a drive current that is adjusted upwards.Similarly, the LED that received the lowest drive current Id2 in thefirst event E will, in the subsequent event E, receive a drive currentthat is adjusted downwards.

In FIG. 8, the flash timing is adjusted in a subsequent event. Thediagram shows that the LED that received the highest drive current Id1(or longest duty cycle) in the first event will be driven for a slightlylonger time to compensate for its poorer performance in the subsequentflash event. Similarly, the LED that received the lowest drive currentId2 (or shortest duty cycle) in the first event E will, in thesubsequent event E, be driven for a slightly shorter time. Thesecorrections for “hot” and “cold” flash segments result in the desiredilluminance distribution P.

In FIG. 9, a flash event E is followed shortly after by a dummy flashevent E_(D). In the dummy flash event E_(D), the adjusted LED drivecurrents Id1_a, Id2_a are the complement of the LED drive currents Id1,Id2 for the active flash event E. The LED that received the higher drivecurrent will now receive a lower drive current, and vice versa. Thiseffectively “forces” a return towards temperature equilibrium over theentire array. The dummy flash event E_(D) takes place within therelatively short time t_(D), which is shorter than the interval Teqrequired for the segmented flash to return to an equilibrium conditionas indicated in FIG. 7. The dummy flash event E_(D) allows correction ofcolour shift between flash segments of a matrix for which the LEDs allhave the same colour.

FIG. 10 shows successive flash events E scheduled using a prior artmethod. Here, there is no compensation for any possible temperaturedifferential during a subsequent flash event E, and the LEDs receive thesame drive currents Id1, Id2 in each flash event E. The “hotter” LEDsmay fail to deliver the desired brightness, however, and a brightnessdelta or colour shift may be noticeable in the subsequent image,particularly in the case when one or more flash segments comprise LEDsof different colours that are mixed “in scene” when the flash segment isturned on. Although the present invention has been disclosed in the formof preferred embodiments and variations thereon, it will be understoodthat numerous additional modifications and variations could be madethereto without departing from the scope of the invention. For example,besides the flash applications described above, video lighting maybenefit from similar current corrections or duty cycle corrections of amulti-segment video light.

For the sake of clarity, it is to be understood that the use of “a” or“an” throughout this application does not exclude a plurality, and“comprising” does not exclude other steps or elements. The mention of a“unit” or a “module” does not preclude the use of more than one unit ormodule.

REFERENCE SIGNS

-   segmented flash system 1-   voltage measuring module 1A-   depth map module 1B-   controller 1C-   segmented flash 10-   light source 100, 100A, 100B-   flash driver 11-   state machine 110-   multiplexer 111-   analog-to-digital converter 112-   memory 113-   current sources 114-   digital-to-analog converter 115-   memory 116-   interface 117-   oscillator 118-   counter 119-   processor 120-   scene 2-   prior art segmented flash system 3-   controller 320-   image sensor 4-   flash segment S1, S2, . . . , Sn-   forward voltage Vf1, Vf2, . . . , Vfn-   flash event E-   dummy flash event E_(D)-   time interval T_(eq)-   drive current Id1, Id2-   adjusted drive current Id1_a, Id2_a, . . . , Idn_a-   illumination profile P

What is claimed is:
 1. A segmented flash system, comprising: an array oflight emitting diodes (LEDs), the LEDs of the array of LEDs beingconfigured to illuminate respective regions of a scene; a voltagemeasuring module configured to measure forward voltages of respectiveLEDs of the array of LEDs, the forward voltages being dependent onrespective temperatures of the respective LEDs of the array of LEDs; anda controller configured to: receive the forward voltages; receive anillumination profile; compute drive power values based on theillumination profile and the forward voltages, the drive power valuesconfigured to at least partially compensate for at least one oftemperature-related illuminance difference or temperature-related colorshift across the array of LEDs; and provide the drive power values tothe LEDs of the array of LEDs to generate a flash to illuminate thescene.
 2. The segmented flash system of claim 1, wherein the controlleris further configured to compute the drive power values such that thedrive power values increase with increasing forward voltage values. 3.The segmented flash system of claim 1, wherein the controller isconfigured to compute each drive power value by adjusting a currentvalue and using a predetermined duty cycle.
 4. The segmented flashsystem of claim 1, wherein the controller is configured to compute eachdrive power value by adjusting a duty cycle and using a predeterminedcurrent value.
 5. The segmented flash system of claim 1, wherein thevoltage measuring module is configured to measure the forward voltageswhile the LEDs of the array of LEDs receive a same constant value ofcurrent.
 6. The segmented flash system of claim 1, wherein the voltagemeasuring module includes: an analog-to-digital converter; a multiplexerthat connects each LED of the array of LEDs to the analog-to-digitalconverter to provide analog measurements of the forward voltages to theanalog-to-digital converter; and a plurality of registers that arecoupled to the analog-to-digital converter, the plurality of registersbeing configured to store digital values that correspond to the analogmeasurements of the forward voltages.
 7. The segmented flash system ofclaim 6, wherein the controller includes: a processor configured todetermine at least one of an amplitude or a timing of one of the drivepower values based on the digital values stored in the registers; and astate machine configured to control the multiplexer and theanalog-to-digital converter to measure the forward voltages and storethe digital values in the registers after a flash event.
 8. Thesegmented flash system of claim 1, wherein computation of the drivepower values includes determination of at least one of a depth map or athree-dimensional (3D) profile of the scene.
 9. A method for operating asegmented flash system, the segmented flash system including an array oflight emitting diodes (LEDs), the LEDs of the array of LEDs beingconfigured to illuminate respective regions of a scene, the methodcomprising: measuring forward voltages of respective LEDs of the arrayof LEDs, the forward voltages being dependent on respective temperaturesof the respective LEDs of the array of LEDs; receiving an illuminationprofile for illuminating the scene; computing drive power values basedon the illumination profile and the forward voltages, the drive powervalues configured to at least partially compensate for at least one oftemperature-related illuminance difference or temperature-related colorshift across the array of LEDs; and providing the drive power values tothe LEDs of the array of LEDs to generate a flash to illuminate thescene.
 10. The method of claim 9, further comprising computing the drivepower values such that the drive power values increase with increasingforward voltage values.
 11. The method of claim 9, further comprisingcomputing each drive power value by adjusting a current value and usinga predetermined duty cycle.
 12. The method of claim 9, furthercomprising computing each drive power value by adjusting a duty cycleand using a predetermined current value.
 13. The method of claim 9,further comprising measuring the forward voltages while the LEDs of thearray of LEDs receive a same constant value of current.
 14. The methodof claim 9, further comprising: providing analog measurements of theforward voltages to an analog-to-digital converter; converting theanalog measurements to digital values with the analog-to-digitalconverter; and storing the digital values.
 15. A segmented flash system,comprising: a light emitting diode (LED) array, the LED array includinga plurality of individually controllable LED segments; a flash driverconfigured to control the LED array; a processor configured to cause theflash driver to controllably apply current to at least some of the LEDsegments in the plurality of LED segments; and memory includinginstructions that, when executed by the processor, cause the processorto perform operations, the operations comprising: generating a firstflash by causing the flash driver to electrically power at least one LEDsegment of the plurality of LED segments; after generating the firstflash, determining forward voltages of the LED segments of the pluralityof LED segments; receiving an illumination pattern; and generating asecond flash by causing the flash driver to electrically power the LEDsegments of the plurality of LED segments based at least in part on theillumination pattern and the forward voltages.
 16. The segmented flashsystem of claim 15, wherein the LED segments are configured to beelectrically powered to at least partially compensate for shifts incolor profile that arise from differences in temperature among the LEDsegments of the plurality of LED segments, the forward voltages beingindicative of respective temperatures of the LED segments of theplurality of LED segments.
 17. The segmented flash system of claim 15,wherein the operations further comprise: calculating drive currents forthe LED segments of the plurality of LED segments based at least in parton the illumination pattern and the forward voltages, the calculateddrive currents increasing with increasing forward voltages; and causingthe flash driver to direct the calculated drive currents to the LEDsegments of the plurality of LED segments.
 18. The segmented flashsystem of claim 15, wherein the operations further comprise: calculatingduty cycles for the LED segments of the plurality of LED segments basedat least in part on the illumination pattern and the forward voltages,the calculated duty cycles increasing with increasing forward voltages;and causing the flash driver to direct current having the calculatedduty cycles to the LED segments of the plurality of LED segments. 19.The segmented flash system of claim 15, wherein the operations furthercomprise: causing the flash driver to direct a same current value to theLED segments of the plurality of LED segments; and measuring the forwardvoltages of the LED segments of the plurality of LED segments while theflash drive is directing the same current value to the LED segments ofthe plurality of LED segments.
 20. The segmented flash system of claim15, wherein: the LED segments in the plurality of LED segments areconfigured to illuminate respective portions of a scene; and the secondflash is configured to illuminate the scene with the illuminationpattern and with illumination having a uniform color profile.